Optical disk and its manufacturing method

ABSTRACT

An optical disk ( 10 ) of the present invention has a substrate ( 11 ) included a resin-impregnated paper, in which resin is impregnated into paper, or resin-coated paper, in which the paper surface is coated with a resin, and a recording layer ( 13 ) formed on at least one side of the substrate ( 11 ). This type of optical disk ( 10 ) has performance equal to that of conventional optical disks and has a minimal effect on the environment during disposal. In addition, a manufacturing method of an optical disk of the present invention has a recording layer sheet fabrication step in which a recording layer sheet is fabricated by forming tracks on a recording layer base material, and a recording layer sheet lamination step in which a recording layer ( 13 ) included the recording layer sheet is provided on a substrate ( 11 ) included resin-impregnated paper or resin-coated paper by laminating the recording layer sheet with the resin-impregnated paper in which a resin is impregnated into paper or the resin-coated paper in which the surface of the paper is coated with a resin. This type of manufacturing method of an optical disk allows optical disk ( 10 ) to be produced inexpensively.

TECHNICAL FIELD

The present invention relates to an optical disk such as a Blu-ray disk(BD) or digital versatile disk (DVD) and manufacturing method of thesame.

BACKGROUND ART

Polycarbonate, epoxy resin and so forth have frequently been used as thesubstrate materials of conventional optical disks since these substratematerials are required to have low contents of extraneous materials andimpurities, high permeability and low double refractive index to enablestable reading and writing, a low moisture absorption rate and superiorheat resistance to prevent deformation of the optical disk, as well ashigh fluidity and superior mold release to facilitate molding processing(Japanese Unexamined Patent Application, First Publication No.05-258349).

However, since bisphenol A is used as monomer for the aforementionedpolycarbonate and epoxy resin substrate materials, unreacted bisphenol Aremained even after polymerization. Due to the growing interest inenvironmental issues in recent years, materials containing bisphenol Ahave tended to be shunned, and studies have been conducted on substratematerials that do not contain bisphenol A.

The use of glass has been considered for use as a substrate materialsince it does not contain bisphenol A and satisfactory opticalcharacteristics in the form of high transmittance. However, glasssubstrates have problems in terms of strength in that they are unable toaccommodate the pressure and stress during production and use due tolimitations on disk thickness.

Another problem with conventional optical disks is that, although silkscreen printing has mainly been used in the case of printing charactersor images on the surface, there is the problem of the difficulty inobtaining highly detailed images with silk screen printing.

In addition, in the case of silk screen printing, in order to printserial numbers or other different characters and images for each disk,it is necessary to change the form plate each time, thereby resulting inthe problem of being unable to in fact impart variable information byprinting to conventional optical disks.

Accordingly, an object of the present invention is to provide an opticaldisk, and manufacturing method of the same, which has performance equalto that of conventional optical disks and has a minimal effect on theenvironment during disposal.

In addition, another object of the present invention is to provide anoptical disk on which highly detailed images are printed, andmanufacturing method of an optical disk that enables highly detailedimages to be printed inexpensively and impart variable information byprinting.

DISCLOSURE OF THE INVENTION

An optical disk of the present invention has a substrate includedresin-impregnated paper in which a resin has been impregnated into paperor resin-coated paper in which the paper surface has been coated with aresin, and a recording layer provided on at least one side of thesubstrate. Since this type of optical disk uses resin-impregnated paperin which a resin has been impregnated into paper or resin-coated paperin which the paper surface has been coated with a resin for thesubstrate, it has a minimal effect on the environment during disposalwhile having performance equal to that of conventional optical disks.

Here, the centerline average roughness Ra of at least one side of thesubstrate is preferably 0.5 μm or less, and the maximum roughness Rmaxis preferably 6.0 μm or less.

In addition, if a printing layer is additionally provided on the sideopposite from the side of the substrate provided with the recordinglayer, then water absorption and moisture absorption of the substratecan be suppressed, and warping and other deformation of the optical diskcan be suppressed.

Similarly, if the aforementioned recording layer is provided on bothsides of the substrate, then water absorption and moisture absorption ofthe substrate can be suppressed, and warping and other deformation ofthe optical disk can be suppressed.

In addition, if the substrate additionally has a protective layer thatprotects the aforementioned recording layer, then together withpreventing scratching of the recording layer, water absorption andmoisture absorption of the substrate can be further suppressed, andwarping and other deformation of the optical disk can be furthersuppressed.

In addition, if the aforementioned recording layer has a recording layerbase material that serves as a support for the recording layer, and thatrecording layer base material includes a non-hydrophilic film, then thewater absorption and moisture absorption of the substrate can be furthersuppressed, and warping and other deformation of the optical disk can befurther suppressed.

In addition, if the aforementioned printing layer has a printing basematerial that serves as a support for the printing layer, and thatprinting base material includes a non-hydrophilic film, then the waterabsorption and moisture absorption of the substrate can be furthersuppressed, and warping and other deformation of the optical disk can befurther suppressed.

In addition, if a release layer is provided between the substrate andthe recording layer and/or printing layer, since the substrate andrecording layer and/or printing layer can be separated and disposed ofseparately at the time of disposal, each layer can be disposed of inaccordance with the material of which it is made, thereby making itpossible to further reduce the effect on the environment.

In addition, manufacturing method of an optical disk of the presentinvention has a recording layer sheet fabrication step in which arecording layer sheet is fabricated by forming tracks on a recordinglayer base material; and, a recording layer sheet lamination step inwhich a recording layer included the recording layer sheet is providedon a substrate included resin-impregnated paper or resin-coated paper bylaminating the recording layer sheet with resin-impregnated paper inwhich a resin is impregnated into paper or resin-coated paper in whichthe surface of the paper is coated with a resin.

In addition, manufacturing method of an optical disk of the presentinvention also preferably has a printing sheet fabrication step in whicha printing sheet is fabricated by carrying out printing on a printingbase material; and, a printing sheet lamination step in which a printinglayer included the printing sheet is provided on a substrate composed ofresin-impregnated paper or resin-coated paper by laminating the printingsheet with resin-impregnated paper in which a resin is impregnated intopaper or resin-coated paper in which the surface of the paper is coatedwith a resin.

In addition, the manufacturing method of an optical disk of the presentinvention also preferably has a protective film lamination step in whicha protective layer included a protective film is provided on therecording layer by laminating the protective film onto the recordinglayer.

In addition, the manufacturing method of an optical disk of the presentinvention also preferably has a release layer formation step in which arelease layer is formed on at least one side of the resin-impregnatedpaper or resin-coated paper in advance.

In this type of the manufacturing method of an optical disk, since thesubstrate, recording layer and as necessary, printing layer andprotective layer, are formed by prefabricating their correspondingsheets followed by their lamination, an optical disk having littlesubstrate warping can be produced inexpensively.

In addition, since the method has fabricating a printing sheet bycarrying out printing on a printing base material in advance followed bylaminating it to the substrate, highly detailed images can be obtainedinexpensively. In addition, variable information, such as sequentiallychanging serial numbers, that differs for each disk can be imparted byprinting onto the optical disk.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of anoptical disk of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of arecording layer in a playback-only optical disk.

FIG. 3 is a schematic cross-sectional view showing an example of arecording layer in a write-once optical disk.

FIG. 4 is a schematic cross-sectional view showing an example of arecording layer in a rewritable optical disk.

FIG. 5 is a schematic cross-sectional view showing another example of anoptical disk of the present invention.

FIG. 6 is a schematic drawing showing a printing sheet and a recordingsheet.

FIG. 7 is a schematic drawing showing (a) a printing sheet fabricationstep, (b) a substrate sheet fabrication step, and (c) a recording layersheet fabrication step.

FIG. 8 is a schematic drawing showing the lamination steps for eachsheet.

FIG. 9 is a schematic cross-sectional view showing another example of anoptical disk of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An optical disk of the present invention has a substrate composed ofresin-impregnated paper in which a resin is impregnated into paper orresin-coated paper in which the surface of the paper is coated with aresin, a recording layer provided on at least one side of saidsubstrate, and as necessary a printing layer or different recordinglayer on the side opposite from the side of the substrate provided withthe recording layer, and additionally as necessary a release layerbetween the substrate and the recording layer.

Specific examples of the layer composition of an optical disk of thepresent invention include: (1) recording layer/substrate, (2) recordinglayer/substrate/printing layer, (3) recording layer/substrate/recordinglayer, (4) protective layer/recording layer/substrate/printing layer,(5) protective layer/recording layer/substrate/protective layer, (6)protective layer/recording layer/substrate/recording layer/protectivelayer, (7) protective layer/recording layer/releaselayer/substrate/printing layer, (8) protective layer/recordinglayer/release layer/substrate/release layer/printing layer, and (9)protective layer/recording layer/release layer/substrate/releaselayer/recording layer/protective layer. Here, a pressure-sensitiveadhesive layer for laminating each layer may be provided between eachlayer as necessary. In particular, that having a recording layer on oneside of the substrate and a printing layer on the other side, or thathaving a recording layer on both sides of the substrate are preferablesince the water absorption and moisture absorption of a substratecomposed of resin-impregnated paper can be suppressed as a result ofboth sides of the substrate being covered.

The following provides an explanation of an optical disk having thelayer composition of (4) above with reference to the drawings.

FIG. 1 is schematic cross-sectional view showing an example of anoptical disk of the present invention. This optical disk 10 is roughlycomposed of a substrate 11 composed of resin-impregnated paper orresin-coated paper, a recording layer 13 laminated on one side ofsubstrate 11 with a pressure-sensitive adhesive layer 12 interposedbetween, a printing layer 15 laminated on the other side of substrate 11with a pressure-sensitive adhesive layer 14 interposed between, and aprotective layer 17 laminated on recording layer 13 with apressure-sensitive adhesive layer 16 interposed between.

<Substrate>

Substrate 11 retains strength required for use as an optical disk, andis required to have rigidity, moisture resistance and water resistance.Consequently, in the present invention, resin-impregnated paper in whicha resin is impregnated into paper or resin-coated paper in which thesurface of the paper is coated with a resin is used for the substrate.Since the paper functions as a reinforcing material, resin-impregnatedpaper and resin-coated paper have adequate rigidity, and since the paperis impregnated with resin or the surface of the paper is coated with aresin, it has moisture resistance and water resistance, superiordimensional stability, little warping and satisfactory surfacesmoothness. In addition, since the material uses paper, it can be easilydisposed of by incineration and so forth, and there is little effect onthe environment at this time.

(Resin-Impregnated Paper)

There are no particular limitations on the paper of theresin-impregnated paper provided it is a paper that uses pulp. Examplesof such paper include 100% virgin pulp paper, coated board papercontaining used paper, and paper that has been clay-coated on one side.In addition, this paper may also be paper produced from wood chipsinstead of pulp, as well as paper produced from non-wood materials suchas kenaf. Moreover, vulcanized fibers may also be used in which the pulphas been bound in gluey form with zinc chloride and so forth. Theapparent specific gravity (basis weight) of these papers is preferably20 to 600 g/m² in consideration of the rigidity of the resin-impregnatedpaper, the ease of impregnation of resin into the paper.

There are no particular limitations on the resin of theresin-impregnated paper provided it does not contain bisphenol A.Examples of such resins include urea formaldehyde resin; melamine resin;polyamide amine and its epichlorhydrin denatured form; latexes such asnatural rubber latex and synthetic rubber latex (such as SBR, NBR, orpolychloroprene); polyvinyl chloride and copolymers of vinyl chlorideand other monomers; polyvinylidene chloride and copolymers of vinylidenechloride and other monomers; acrylic resin; polyester; and polyolefinssuch as polyethylene and polypropylene.

In addition, the resin of the resin-impregnated paper may be apolyisocyanate resin obtained by impregnating polyisocyanate into paperand allowing the polyisocyanate to react with the moisture in the paper.Examples of polyisocyanates include aromatic diisocyanates such asphenylene diisocyanate (PDI), tolylene diisocyanate (TDI), naphthalenediisocyanate (NDI), 4,4′-diisocyanate diphenylmethane (MDI), ortetramethylxylene diisocyanate; aromatic aliphatic diisocyanates such asxylylene diisocyanate (XDI); hydrogenated TDI, hydrogenated MDI, andhydrogenated XDI; aliphatic or alicyclic diisocyanates such ashexamethylene diisocyanate (HMDI) and isophorone diisocyanate and theirpolyol derivatives or their burette forms; trimers of the aforementioneddiisocyanates; trifunctional isocyanates such as lysine triisocyanate(LTI) and triphenylmethane triisocyanate; and oligomers or polymershaving an isocyanate group.

In addition, the resin of the resin-impregnated paper may be a silaneresin obtained by impregnating a silane coupling agent into paper andallowing the silane coupling agent to react with moisture in the paperin the presence of an acid catalyst. In addition, a polyol may be addedto the silane coupling agent and the silane coupling agent may then beallowed to react therewith. Examples of silane coupling agents includeethyl trimethoxysilane, tetraethoxysilane, vinyl trimethoxysilane,γ-chloropropylmethyl dimethoxysilane, γ-chloropropyl trimethoxysilane,glycidoxypropyl trimethoxysilane, γ-methacryloxypropyl trimethoxysilaneand γ-methacryloxy-propylmethyl dimethoxysilane. Examples of acidcatalysts include hydrochloric acid. Examples of polyols include acrylicpolyol.

Examples of methods for impregnating resin into paper include a methodin which paper is immersed in a resin solution or liquid resin; a methodin which a resin solution or liquid resin is coated onto paper; a resinin which resin is mixed into pulp during paper production (internaladdition); and a method in which resin is sprayed onto the pulp duringpaper production. Here, an organic solvent such as alcohol forpreventing moisture absorption by the paper is preferable for thesolvent of the resin solution. In addition, in the case of coating aresin solution or liquid resin onto paper, it is preferably coated ontoboth sides of the paper.

The amount of resin impregnated (dry weight excluding organic solvent)is preferably 1 to 10% by mass, and more preferably 3 to 10% by mass, inthe resin-impregnated paper (100% by mass) in consideration of therigidity, productivity and ease of disposal of the resin-impregnatedpaper.

Resin-impregnated paper can be obtained after impregnating resin intothe paper by curing, drying or solidifying the resin as necessary.

The thickness of resin-impregnated paper obtained in this manner ispreferably 0.5 to 1.6 mm in consideration of optical disk strength andoptical disk specifications.

(Resin-Coated Paper)

Resin-coated paper is paper in which resin has been coated and/orlaminated onto the paper surface. Examples of resin-coated paper includethat in which a resin solution has been coated onto the paper surface,that in which a thermoplastic resin has been laminated onto the papersurface by a molten lamination method, that in which a UV (photo)-curedresin or electron beam (EB)-cured resin is coated onto the papersurface, that in which a resin film has been laminated onto the papersurface, and that in which a resin solution has been coated onto thepaper surface and a resin film is additionally laminated thereon.

There are no particular limitations on the paper of the resin-coatedpaper provided it is paper that uses pulp. The same paper used for theresin-impregnated paper can be used for this type of paper.

There are no particular limitations on the resin of the resin-coatedpaper provided it does not contain bisphenol A.

Examples of resins of resin solutions for coating include ureaformaldehyde resin, melamine resin, polyamide amine and itsepichlorhydrin denatured form, latexes such as natural rubber latex andsynthetic rubber latexes (such as SBR, NBR, or polychloroprene),polyvinyl chloride, copolymers of vinyl chloride and other monomers,polyvinylidene chloride, copolymers of vinylidene chloride and othermonomers, polyvinyl alcohol resin, polyacrylamide, acrylic resin,polyester, and polyolefins such as polyethylene and polypropylene.

Examples of thermoplastic resins used in molten lamination methodsinclude polyethylene, polypropylene, and polyester.

Examples of UV (photo)-cured or electron beam (EB)-cured resins includeepoxy acrylate, urethane acrylate, polyester acrylate, and polyetheracrylate.

Examples of resin films include polyester films such as polyethyleneterephthalate and polyethylene naphthalate, polyethylene, polyolefinfilms such as polypropylene, polystyrene film, polyamide film, polyvinylchloride film, polyacrylnitrile film, polyamide film, polylactic acidfilm, triacetylcellulose film, and cyclic polyolefin film.

Resin-coated paper can be obtained after coating and/or laminating resinonto the paper surface by curing, drying or solidifying the resin asnecessary.

The thickness of resin-coated paper obtained in this manner ispreferably 0.5 to 1.6 mm in consideration of optical disk strength andoptical disk specifications.

(Surface Smoothness)

Substrate 11 is required to have surface smoothness in order to use asan optical disk. The centerline average roughness Ra (JIS B 0601) of atleast one side of substrate 11 is preferably 0.5 μm or less, and themaximum roughness Rmax (JIS B 0601) is preferably 6.0 μm or less. Inaddition, it is particularly preferable that the centerline averageroughness Ra and maximum roughness Rmax of both sides of substrate 11 bewithin the aforementioned ranges.

Examples of methods for imparting surface smoothness to substrate 11include a method in which a resin film having superior smoothness islaminated on the surface of the paper, a method in which surfacetransfer of a material having superior surface smoothness (such asglass, film, ceramics or metal) is carried out after impregnating orcoating resin onto the paper, and a method in which resin-impregnatedpaper or resin-coated paper is hot-pressed.

(Peripheral Edge Protection)

Deformation prevention effects can be maintained by protective treatmentof the peripheral edges of substrate 11. The peripheral edges ofsubstrate 11 are protected by resin coating or by attaching a resincover. Examples of resins used in the case of resin coating include ureaformaldehyde resin, melamine resin, polyamide amine and itsepichlorhydrin denatured form, latexes such as natural rubber latex andsynthetic rubber latex such as SBR, NBR and polychloroprene, polyvinylchloride, copolymers of vinyl chloride and other monomers,polyvinylidene chloride, copolymers of vinylidene chloride and othermonomers, polyvinyl alcohol resin, polyacrylamide, acrylic resin,polyester, and polyolefins such as polyethylene and polypropylene.

Examples of resins of resin covers include polyolefins such aspolyethylene and polypropylene, polyvinyl chloride, copolymers of vinylchloride and other monomers, polyvinylidene chloride, copolymers ofvinylidene chloride and other monomers, polystyrene, ABS plastic,methacrylic resin, epoxy resin, unsaturated polyester resin, phenolresin and melamine resin.

<Recording Layer>

Recording layer 13 is a layer on which information is recorded and/or alayer on which information can be recorded, and is able to record and/orread information by being irradiated with light.

Recording layer 13 includes that on which information has been recordedin advance at the time of optical disk production, and that on whichinformation can be recorded after production, and is normally classifiedinto one of three types consisting of: (1) that on which information isrecorded in advance at the time of optical disk production but on whichinformation cannot be recorded after production (playback-only type);(2) that on which information is not recorded at the time of opticaldisk production but on which information can be recorded afterproduction (write-once type); and, (3) that from which recordedinformation can be erased and on which information can be re-recorded(rewritable type).

The following provides a detailed explanation of each type of recordinglayer.

(Playback-Only Type)

FIG. 2 is a cross-sectional view showing an example of a playback-onlytype of recording layer. This recording layer 13 is roughly composedhaving a recording layer base material 31, an information pit forminglayer 32 having irregularities in its surface formed on recording layerbase material 31, and a light reflecting layer 33 that covers thesurface irregularities of information pit forming layer 32, and the sidehaving recording layer base material 31 contacts a pressure-sensitiveadhesive layer 12 (not shown), while the side having light reflectinglayer 33 contacts a pressure-sensitive adhesive layer 16.

Recording layer base material 31 serves as a support of recording layer13. A resin film is normally used for recording layer base material 31.There are no particular limitations on the resin film provided it is afilm composed of a resin that does not contain bisphenol A. The resinfilm is preferably a non-hydrophilic film in consideration ofsuppressing the water absorption and moisture absorption of substrate11.

Preferable examples of a non-hydrophilic film in particular includepolyolefin films composed of low density polyethylene (LDPE), linear lowdensity polyethylene (LLDPE), high density polyethylene (HDPE),polypropylene, non-crystalline cyclic polyolefins, tetracyclododecenepolymers or cycloolefin polymers in consideration of enabling disposalby incineration and minimal effects on the environment as a result ofbeing decomposed into water and carbon dioxide by incineration.

In addition, a biodegradable resin film is preferable for thenon-hydrophilic film in consideration of minimal effects on theenvironment as a result of being decomposed by microbes in the soil andso forth even if disposed directly. Polylactic acid resin, for example,can be used as a biodegradable resin. Examples of polylactic acid resinsinclude “Ecoloju” manufactured by Mitsubishi Plastics Inc., “Terramac”manufactured by Unitika, Ltd., and “Palgreen LC” manufactured byTohcello Co., Ltd. In addition, copolymer polyesters of polyvalentalcohols such as 1,4-butadiol and pentaerythritol, and succinic acid oradipic acid, for example, can also be used as biodegradable resins.Examples of this type of biodegradable polyester resins include “Biomax”manufactured by DuPont and “Bionolle” manufactured by Showa High PolymerCo., Ltd.

The thickness of the resin film is preferably 30 μm or more inconsideration of maintaining the strength of a support.

Information pit forming layer 32 has irregularities in its surface, andtracks and information pits are represented by these surfaceirregularities. Information pit forming layer 32 is the result of curingan ultraviolet-cured resin in which a photoinitiator is combined with anoligomer or monomer such as urethane acrylate oligomer, polyesteracrylate oligomer or low-viscosity acrylic monomer; and curing anelectron beam-cured resin such as urethane-denatured acrylate resin andacrylic-denatured polyester resin. However, it is preferable not to usean epoxy resin that contains bisphenol A.

The thickness of information pit forming layer 32 is normally 20 to 80nm.

Light reflecting layer 33 is provided along the surface irregularitiesof information pit forming layer 32 and reflects irradiated light. Lightreflecting layer 33 is a thin film composed of a metal such as aluminum,aluminum alloy, silver or silver alloy formed by, for example, vacuumdeposition or sputtering.

The thickness of light reflecting layer 33 is normally 10 to 100 nm, andthe thickness is preferably uniform.

(Write-Once Type)

FIG. 3 is a cross-sectional view showing an example of a write-once typeof recording layer. This recording layer 13 is roughly composed having arecording layer base material 41, an information track forming layer 42having irregularities in its surface formed on the surface of recordinglayer base material 41, a light reflecting layer 43 that covers thesurface irregularities of information track forming layer 42, andinformation pit recording layer 44 formed on the surface of lightreflecting layer 43, and the side of recording layer base material 41contacts a pressure-sensitive adhesive layer 12 (not shown), while theside of information pit recording layer 44 contacts a pressure-sensitiveadhesive layer 16.

Recording layer base material 41 serves as a support of recording layer13. The same resin films as the aforementioned recording layer basematerial 31 can be used for recording layer base material 41.

Information track forming layer 42 has irregularities in its surfacehaving a depth of 50 to 110 nm, and tracks are represented by thesesurface irregularities. However, differing from a playback-only type,information pits are not formed. A cured ultraviolet-cured resin orelectron beam-cured resin can be used in the same manner as theaforementioned information pit forming layer 32 for information trackforming layer 42.

Light reflecting layer 43 is provided along the surface irregularitiesof information track forming layer 42, and reflects irradiated light.Light reflecting layer 43 is a metal thin film formed by vacuumdeposition or sputtering in the same manner as the aforementioned lightreflecting layer 33.

Information pit recording layer 44 is a colored film composed of, forexample, an organic pigment, and as a result of being irradiated withlaser light for information recording, this portion becomes informationpits where information signals are recorded as a result of undergoing aphysical change (destruction) following the occurrence of a change inthe molecular structure of organic pigment at the irradiated site. Sincethe site where the physical change has occurred decreases in opticaltransmittance, when irradiated with light for reading, the amount ofreflected light from light reflecting layer 43 decreases, and as aresult, information signals can be detected in the same manner as in thecase of surface irregularity pits being formed.

Examples of organic pigments include phthalocyanine pigment,naphthalocyanine pigment, and naphthoquinone pigment.

The thickness of information pit recording layer 44 is normally 50 to200 nm.

(Rewritable Type)

FIG. 4 is a cross-sectional view showing an example of a rewritable typeof recording layer. This recording layer 13 is roughly composed having arecording layer base material 51, an information track forming layer 52having irregularities in its surface formed on the surface of recordinglayer base material 51, a light reflecting layer 53 that covers thesurface irregularities of information track forming layer 52, and aninformation pit forming layer 54 formed on the surface of lightreflecting layer 53, and the side of recording layer base material 51contacts a pressure-sensitive adhesive layer 12 (not shown), while theside of information pit recording layer 54 contacts a pressure-sensitiveadhesive layer 16.

Recording layer base material 51 serves as a support of recording layer13. The same resin films as the aforementioned recording layer basematerial 31 can be used for recording layer base material 51.

Information track forming layer 52 has irregularities in its surfacehaving a depth of 50 to 110 nm, and tracks are represented by thesesurface irregularities. However, differing from a playback-only type,information pits are not formed. A cured ultraviolet-cured resin orelectron bearn-cured resin can be used in the same manner as theaforementioned information pit forming layer 32 for information trackforming layer 52.

Light reflecting layer 53 is provided along the surface irregularitiesof information track forming layer 52, and reflects irradiated light.Light reflecting layer 53 is a metal thin film formed by vacuumdeposition or sputtering in the same manner as the aforementioned lightreflecting layer 33.

Information pit recording layer 54 is a transparent dielectric filmcomposed of three layers consisting of, for example, an SiO₂ film,GeSbTe film and SiO₂ film, and the information pit recording layer shownin the drawing has a bilayer structure laminated in the order of SiO₂film 61, GeSbTe film 62, SiO₂ film 63, GeSbTe film 64 and SiO₂ film 65.

The recording, erasure and reading of information by information pitrecording layer 54 is carried out in the manner described below.

Laser light is focused on a GeSbTe layer to heat this layer followed byrapid cooling to record information by polycrystallizing ordecrystallizing the GeSbTe film. Laser light that is weak enough not toaffect the GeSbTe film is irradiated, the laser light penetrates thepolycrystallized or decrystallized GeSbTe film, and the light reflectedby the light reflecting layer is received allowing information to beread depending on whether or not there is crystallization of the GeSbTefilm. On the other hand, information is erased by crystallizing theGeSbTe film as a result of focusing laser light of a lower intensityonto a polycrystallized or decrystallized GeSbTe film to slowly heat thefilm. This recording and erasure is reversible, and differentinformation can again be recorded after a recording has been erased.

A ZnS—SiO₂ film, Ta₂O₅ film, SiN film or AlN film can be used instead ofan SiO₂ film. In addition, an AgInSbTe film can be used instead of aGeSbTe film.

Each of these films can be formed by sputtering, vacuum deposition andso forth.

The thickness of each film is roughly 10 to 300 nm, and should besuitably set according to the type and number of layers. For example,the thickness of each film of information pit recording layer 54 is 220nm for the SiO₂ film, 13 nm for the GeSbTe film, 25 nm for the SiO₂film, 40 nm for the GeSbTe film and 95 nm for the SiO₂ film in thatorder.

<Printing Layer>

Printing layer 15 is formed by printing by printing ink 22 on printingbase material 21. Here, although printing is carried out on the side ofpressure-sensitive adhesive layer 14, namely the back side of printingbase material 21, this is preferable since in addition to being able toprotect the printed surface composed of printing ink 22, unique imageshaving both luster and depth can be obtained.

A resin film is normally used for printing base material 21. There areno particular limitations on the resin film provided it is a film thatdoes not contain bisphenol A. A non-hydrophilic film is preferable forthe resin film since it suppresses water absorption and moistureabsorption of substrate 11.

Preferable examples of a non-hydrophilic film in particular includepolyolefin films in consideration of enabling disposal by incinerationand minimal effects on the environment as a result of being decomposedinto water and carbon dioxide by incineration. In addition, abiodegradable resin film is preferable for the non-hydrophilic film inconsideration of minimal effects on the environment as a result of beingdecomposed by microbes in the soil and so forth even if disposed ofdirectly.

The same films as those used in the aforementioned recording layer basematerial 31 can be used for the polyolefin film and biodegradable resinfilm.

The thickness of printing base material 21 is normally 12 to 80 μm.

There are no particular limitations on printing ink 22 provided it doesnot contain bisphenol A. An example of printing ink 22 is a printing inkhaving a biodegradable resin such as polylactic acid resin as a binderwhile also containing various types of additives in consideration ofminimal effects on the environment during disposal. Examples ofadditives include coloring pigments, pigment dispersants and viscosityadjusters.

Examples of characters and images formed by printing include markingsthat at least indicate the type of optical disk, additional informationrelating to the optical disk (such as manufacturer, retailer, price,storage capacity and usage precautions), and full-color decorativeimages having intermediate gradations (such as images of the recordedinformation). In addition, an area enabling the writing of additionalinformation with a pencil, ballpoint pen or ink jet printer and so forthmay also be provided.

<Protective Layer>

Protective layer 17 protects the surface of recording layer 13 andprevents damage to the recording layer. In addition, protective layer 17also fulfills the role of suppressing water absorption and moistureabsorption of substrate 11.

Since it is necessary for protective layer 17 to allow light irradiatedonto the optical disk to penetrate to recording layer 13, it ispreferably a resin film having high optical transmittance. In addition,preferable examples of resin films include polyolefin films andbiodegradable resin films in consideration of minimal effects on theenvironment during disposal.

The same films used for the aforementioned recording layer base material31 can be used for the polyolefin film and biodegradable resin film.

The thickness of protective layer 17 is normally 0.03 to 1.0 mm, andpreferably 0.1 to 0.6 mm.

Furthermore, protective layer 17 may be composed by directly coating aliquid ultraviolet-cured resin, electron beam-cured resin, and so forthonto recording layer 13 by spin coating without using apressure-sensitive adhesive layer 16 to be described later, followed bythe curing thereof.

<Pressure-Sensitive Adhesive Layers>

Pressure-sensitive adhesive layers 12, 14 and 16 are for laminating eachlayer, and are layers composed of a pressure-sensitive adhesive. Acrylicpressure-sensitive adhesives and other known pressure-sensitiveadhesives can be used for the pressure-sensitive adhesive.

The amount of pressure-sensitive adhesive should be suitably determinedaccording to the material of each layer to be laminated. It ispreferable that pressure-sensitive adhesive layer 12 laminated betweensubstrate 11 and recording layer 13 have a smooth surface on the side ofrecording layer 13.

<Release Layers>

As shown in FIG. 5, an optical disk of the present invention may be anoptical disk 20 in which release layers 18 and 19 are provided betweensubstrate 11 and recording layer 13 and between substrate 11 andprinting layer 15 for separation of each layer during disposal.

Release layers 18 and 19 are preferably made of materials having lowlevels of surface activity, examples of which include polyolefins suchas polyethylene and polypropylene.

The thickness of release layers 18 and 19 is normally 5 μm to 1 mm.

<Optical Disk Production Process>

The following provides an explanation of a process for producing anoptical disk of the present invention.

An optical disk production process of the present invention is a processfor producing an optical disk consisting of producing a printing layer,substrate, recording layer and protective layer separately with eachsheet-like member wound as shown in FIG. 6, coating a pressure-sensitiveadhesive in a predetermined order in the final step, and then pressingand laminating them together to obtain the desired layer compositionfollowed by punching out into the shape of a disk.

The following provides an explanation of an example of a productionprocess of optical disk 20 having the layer composition shown in FIG. 5.

A printing sheet is fabricated in advance by printing onto printing basematerial 21 (printing sheet fabrication step), release layers 18 and 19are formed on both sides of resin-impregnated paper (release layerformation step), and a recording layer sheet is fabricated by formingtracks on recording layer base material 31 (41 or 51) (recording layersheet fabrication step). Next, a printing layer 15 composed of theprinting sheet is provided on substrate 11 composed of resin-impregnatedpaper by laminating resin-impregnated paper and the aforementionedprinting sheet (printing sheet lamination step), recording layer 13composed of the printing layer sheet is provided on substrate 11composed of resin-impregnated paper by laminating resin-impregnatedpaper and the aforementioned recording layer sheet (recording layersheet lamination step), and protective layer 17 composed of a protectivefilm is provided on recording layer 13 by laminating a protective filmon recording layer 13 (protective film lamination step) to form a rollhaving the desired layer composition followed by punching out said rollinto the shape of disks to produce optical disk 20.

<Printing Sheet Fabrication Step>

A printing sheet is fabricated by carrying out printing by printing ink22 on printing base material 21 according to the step shown in FIG. 7Afollowed by winding onto a roller. At this time, positioning patternsare printed onto the printing sheet as shown in FIG. 6.

Examples of printing methods include offset printing, gravure printing,relief printing, screen printing, ink jet printing andelectrophotography. Offset printing or gravure printing is particularlypreferable in the case of full-color printing having intermediategradations since these methods allow the obtaining of high-definitionimages. In addition, ink jet printing or electrophotography ispreferable in the case of imparting variable information that differsfor each disk.

<Release Layer Formation Step>

Release layers 18 and 19 are formed in advance on resin-impregnatedpaper serving as substrate 11 by molten extrusion coating of apolyolefin such as polyethylene onto both of its sides according to thestep shown in FIG. 7( b). The resin-impregnated paper on which releaselayers 18 and 19 are formed (to also be referred to as a substratesheet) is wound into the shape of a roll.

<Recording Layer Sheet Fabrication Step>

A recording layer sheet is fabricated by forming tracks on recordinglayer base material 31 (41 or 51), forming various layers respectivelycorresponding to a playback-only type, write-once type or rewritabletype, and winding into the shape of a roll according to the step shownin FIG. 7( c). At this time, positioning patterns (surfaceirregularities and so forth) are formed in the printing layer sheet asshown in FIG. 6.

(Playback-Only Type)

First, an ultraviolet-cured resin is coated onto recording layer basematerial 31, and a transfer mold having surface irregularitiescorresponding to tracks and information pits is pressed against itssurface to transfer the surface irregularities to the surface of theultraviolet-cured resin (embossing processing). Next, theultraviolet-cured resin is cured by irradiating with ultraviolet lightto form information pit forming layer 32. At this time, by using atransfer mold having a diffraction grating pattern or hologram patternin addition to the surface irregularities corresponding to tracks andinformation pits for the transfer mold, an anti-theft or other patterncan also be formed on information pit forming layer 32.

Next, light reflecting layer 33 composed of a metal thin film is formedon information pit forming layer 32 by vacuum deposition or sputtering.

(Write-Once Type)

The formation of information track forming layer 42 and light reflectinglayer 43 is carried out in the same manner as information pit forminglayer 32 and light reflecting layer 33 of the playback-only type.However, a transfer mold that does not have surface irregularitiescorresponding to information pits is used for the transfer mold.

Next, an organic pigment is coated onto light reflecting layer 43 toform information pit recording layer 44 composed of an organic pigmentcolored film. Examples of coating methods include gravure coating,microgravure coating, die coating, comma coating, air knife coating androll coating.

(Rewritable Type)

The formation of information track forming layer 52 and light reflectinglayer 53 is carried out in the same manner as the write-once type.

Next, SiO₂ film 61, GeSbTe film 62, SiO₂ film 63, GeSbTe film 64 andSiO₂ film 65 are sequentially formed on light reflecting layer 53 bysputtering or vacuum deposition.

<Lamination Steps>

As shown in FIG. 8, a pressure-sensitive adhesive is first coated on theprinted side of a printing sheet, and this is laminated with a substratesheet (resin-impregnated paper on which a release layer is formed).

Next, a pressure-sensitive adhesive is coated onto a recording layersheet and this is laminated onto the other side of the substrate sheetto which the printing sheet has been laminated. At this time, theprinting sheet and recording layer sheet are positioned by reading thepositioning patterns on the printing sheet and the positioning patternson the recording layer sheet with a position reading sensor.

Next, a pressure-sensitive adhesive is coated onto a protective sheet,and this is laminated onto recording layer 13 on the substrate sheet toform an optical disk roll.

<Punching Step>

Next, the optical disk-shaped processed portions of the roll aresynchronized with a disk-shaped cutting blade by reading the positioningpatterns with a sampling position reading sensor, and then roll ispunched out in the shape of disks with the disk-shaped cutting blade toobtain optical disks.

Optical disks obtained in this manner can be deformed depending on thematerial of each layer. Accordingly, in order to ensure smoothness, astep may be inserted in which warping of the roll is removed by heatingthe optical disks from both sides with a flat heating plate.

In addition, the shape of the peripheral edges of the optical disks canbe changed in order to sustain the effect of preventing changes causedby environmental changes. The peripheral edge of an optical disk isformed to be curved so that the protective layer and so forth covers theperipheral edge of substrate 11 within a range that does not affect therecording area of the recording layer. The formation of this curvaturecan be carried out by a method such as using a disk-shaped cutting bladethat is able to curve the peripheral edge when punching out the opticaldisk from the roll, or by a method in which the periphery of the opticaldisk is pressed to form a curve after being punched out. As a result offorming this curvature, the area over which the peripheral edge ofsubstrate 11 contacts the outside air can be reduced along theperipheral edge of the optical disk, thereby making it possible tofurther sustain the effect of preventing deformation of the opticaldisk.

In an optical disk of the present invention as has been explained above,since resin-impregnated paper or resin-coated paper is used forsubstrate 11, it can be disposed of easily by incineration or buryingunderground, and there is only a minimal effect on the environment atthat time. In addition, in an optical disk of the present invention,since resin-impregnated paper or resin-coated paper is used forsubstrate 11, the optical disk has the required strength for use as anoptical disk as a result of the paper functioning as a reinforcingmaterial, and since the paper is in the state of being impregnated withresin or the surface of the paper is in the state of being coated withresin, it is resistant to absorption of water and moisture, has superiordimensional stability and demonstrates little warping.

In addition, since printing layer 12 is additionally provided on theside of substrate 11 opposite from the side on which recording layer 13is provided, both sides of substrate 11 are covered, thereby making itpossible to further suppress water absorption and moisture absorption bysubstrate 11, as well as further suppress warping and other deformationof the optical disk.

Action similar to this is also demonstrated even in the case recordinglayer 13 is provided on both sides of the substrate.

In addition, since protective layer 17 that protects recording layer 13is additionally provided, together with preventing recording layer 13from being damaged, water absorption and moisture absorption bysubstrate 11 can be further suppressed, thereby making it possible tofurther suppress warping and other deformation of the optical disk.

In addition, if recording layer 13 has a recording layer base material31 (41 or 51) composed of a non-hydrophilic film, water absorption andmoisture absorption of substrate 11 can be further suppressed, therebymaking it possible to further suppress warping and other deformation ofthe optical disk.

In addition, if printing layer 15 is provided with printing basematerial 21 composed of a non-hydrophilic film, then the waterabsorption and moisture absorption of substrate 11 can be furthersuppressed, thereby making it possible to further suppress warping andother deformation of the optical disk.

In addition, since release layers 18 and 19 are provided betweensubstrate 111 and recording layer 13 and between substrate 11 andprinting layer 15, substrate 11, recording layer 13 and printing layer15 can be separated at the time of disposal and disposed of separately,thereby enabling disposal corresponding to the material of each layerand making it possible for further reduce the effects on theenvironment.

In addition, in an optical disk production process of the presentinvention, since substrate 11, recording layer 13, printing layer 15 andprotective layer 17 are formed by fabricating their corresponding sheetsin advance followed by laminating those sheets, differing from coatingby spin coating and so forth, there is less material waste, anddiffering from the case of preliminarily laminating each layer thatcomposes printing layer 13, recording layer 15 and protective layer 17on a substrate in order, an optical disk having little warping ofsubstrate 11 can be produced inexpensively without being subjected tostress caused by differences in the coefficients of thermal expansion.

In addition, since a method is employed in which printing is carried outin advance on printing base material 21 to fabricate a printing sheetfollowed by laminating this onto substrate 11, high-definition printingcan be carried out, and highly detailed images can be obtainedinexpensively. In addition, serial numbers and other variableinformation that differs for each disk can be printed onto an opticaldisk in the aforementioned printing sheet fabrication step.

Furthermore, an optical disk of the present invention is not limited tothat described in the aforementioned embodiments, but rather the designand so forth may be altered within a range that does not deviate fromthe gist of the present invention.

For example, an optical disk of the present invention is not limited toa disk shape, but may be rectangular or any other arbitrary shapeprovided the region where information is recorded is circular.

In addition, although a pressure-sensitive adhesive is used whenlaminating each layer in the aforementioned embodiments, an adhesivelayer, adhesive material, or a pressure-sensitive adhesive material inwhich a pressure-sensitive adhesive or adhesive has been formed into theshape of a sheet may also be used for the pressure-sensitive adhesive.

In addition, in the aforementioned optical disk production example,although the substrate sheet was wound into a roll, in the case of beingwound into a roll, there are cases in which warping occurs in thesubstrate and the optical disk becomes susceptible to deformation.Accordingly, the substrate sheet may also be in the form of a flat sheetfree of curling instead of a wound roll.

EXAMPLES

The following indicates examples of the present invention.

Example 1

(Fabrication of Printing Sheet)

Gravure printing was carried out using biodegradable polyester printingink (Dainichiseika Color and Chemicals, Biotech Color HGP) on apolylactic acid film drawn to a thickness of 0.04 mm (MitsubishiPlastics, Ecoloju) to obtain a printing sheet on which was printedmarkings indicating the type of optical disk, additional informationrelating to the optical disk, decorative images and so forth.

(Fabrication of Substrate Sheet)

Polyethylene was molten extrusion coated onto both sides ofresin-impregnated paper having a thickness of 1.0 mm (Hokuetsu PaperMills, water-resistant vulcanized fiber) followed by preliminarilyforming a release layer having a thickness of 0.015 mm.

(Fabrication of Recording Layer Sheet)

Surface irregularities corresponding to tracks and information pits weretransferred to a copper-plated roll after which the roll waschrome-plated from above to obtain a transfer mold.

An ultraviolet-cured resin was coated onto a high-density polyethylenefilm drawn to a thickness of 0.05 mm with a die coater to a thickness of0.1 mm, and the transfer mold was pressed against its surface totransfer the surface irregularities to the surface of theultraviolet-cured resin.

Next, the ultraviolet-cured resin was irradiated with ultraviolet lightto cure the ultraviolet-cured resin and form tracks.

Next, aluminum was vacuum deposited on the tracks and a light reflectinglayer having a thickness of 60 nm was formed to obtain a playback-onlytype of recording layer sheet.

(Lamination)

An acrylic pressure-sensitive adhesive was coated onto the printedsurface of the printing sheet to a thickness of 0.005 mm by microgravurecoating after which it was laminated with the substrate sheet.

Next, an acrylic pressure-sensitive adhesive was coated on the recordinglayer sheet to a thickness of 0.005 mm by microgravure coating afterwhich it was laminated onto the other side of the substrate sheet towhich the printing sheet had been laminated.

Next, an acrylic pressure-sensitive adhesive was coated onto aprotective sheet (high-density polyethylene film drawn to a thickness of0.065 mm) to a thickness of 0.005 mm by microgravure coating after whichit was laminated onto the substrate sheet to obtain an optical diskroll.

(Punching)

Next, the optical disk roll was punched into the shape of disks using adisk-shaped cutting blade to obtain optical disks. The optical diskswere subsequently placed between flat plates followed by the applicationof heat at 50° for 24 hours to remove any warping and obtain smoothoptical disks.

(Evaluation)

When information recorded on the resulting optical disks was read usingan optical disk drive manufactured by Pulstec Industrial Co., Ltd.(product name: DDU-1000), the information was able to be read withoutproblem.

In addition, the substrate (+release layer), recording layer(+pressure-sensitive adhesive layer+protective layer) and printing layer(+pressure-sensitive adhesive layer) were able to be separated, and thesubstrate and printing layer were able to be disposed of by buryingunderground. The protective layer was able to be further separated fromthe recording layer (+pressure-sensitive adhesive layer+protectivelayer), and the protective layer was able to be disposed of by buryingunderground. The metal thin film component was recovered from therecording layer.

Example 2

With the exception of changing the fabrication of the recording layersheet as described below, optical disks were obtained in the same manneras Example 1.

(Fabrication of Recording Layer Sheet)

Surface irregularities corresponding to tracks and information pits weretransferred to a copper-plated roll after which the roll waschrome-plated from above to obtain a transfer mold.

An ultraviolet-cured resin was coated onto a high-density polyethylenefilm drawn to a thickness of 0.05 mm with a die coater to a thickness of0.1 mm, and the transfer mold was pressed against its surface totransfer the surface irregularities to the surface of theultraviolet-cured resin.

Next, the ultraviolet-cured resin was irradiated with ultraviolet lightto cure the ultraviolet-cured resin and form tracks.

Next, aluminum was vacuum deposited on the tracks and a light reflectinglayer having a thickness of 60 nm was formed.

Next, a cyanine pigment was coated onto the light reflecting layer bymicrogravure coating to form a colored film having a thickness of 60 nmand obtain a write-once type of recording layer sheet.

(Evaluation)

When information was recorded (writing) and information recorded on theresulting optical disks was read using an optical disk drivemanufactured by Pulstec Industrial Co., Ltd. (product name: DDU-1000),the information was able to be recorded and read without problem.

In addition, the substrate (+release layer), recording layer(+pressure-sensitive adhesive layer+protective layer) and printing layer(+pressure-sensitive adhesive layer) were able to be separated, and thesubstrate and printing layer were able to be disposed of by buryingunderground. The protective layer was able to be further separated fromthe recording layer (+pressure-sensitive adhesive layer+protectivelayer), and the protective layer was able to be disposed of by buryingunderground. The metal thin film component was recovered from therecording layer.

Example 3

With the exception of changing the fabrication of the recording layersheet as described below, optical disks were obtained in the same manneras Example 1.

(Fabrication of Recording Layer Sheet)

Surface irregularities corresponding to tracks were transferred to acopper-plated roll after which the roll was chrome-plated from above toobtain a transfer mold.

An ultraviolet-cured resin was coated onto a high-density polyethylenefilm drawn to a thickness of 0.05 mm with a die coater to a thickness of0.1 mm, and the transfer mold was pressed against its surface totransfer the surface irregularities to the surface of theultraviolet-cured resin.

Next, the ultraviolet-cured resin was irradiated with ultraviolet lightto cure the ultraviolet-cured resin and form tracks.

Next, aluminum was vacuum deposited on the tracks and a light reflectinglayer having a thickness of 60 nm was formed.

Next, an SiO₂ film having a thickness of 220 nm, a GeSbTe film having athickness of 13 μm, an SiO₂ film having a thickness of 25 nm, a GeSbTefilm having a thickness of 40 nm and an SiO₂ film having a thickness of95 nm were sequentially formed by sputtering on the light reflectinglayer to obtain a rewritable type of recording layer sheet.

(Evaluation)

When information was recorded (writing), information recorded on theresulting optical disks was read, the recorded information was erasedand information was then rewritten using an optical disk drivemanufactured by Pulstec Industrial Co., Ltd. (product name: DDU-1000),the information was able to be recorded, read, erased and rewrittenwithout problem.

In addition, the substrate (+release layer), recording layer(+pressure-sensitive adhesive layer+protective layer) and printing layer(+pressure-sensitive adhesive layer) were able to be separated, and thesubstrate and printing layer were able to be disposed of by buryingunderground. The protective layer was able to be further separated fromthe recording layer (+pressure-sensitive adhesive layer+protectivelayer), and the protective layer was able to be disposed of by buryingunderground. The metal thin film component was recovered from therecording layer.

Example 4

An optical disk 70 was fabricated having a substrate 74, in which resinfilms 73 were laminated onto both sides of paper 71 with adhesive layers72 interposed between, a recording layer 75 laminated onto one side ofsubstrate 74 with a pressure-sensitive adhesive layer (not shown)interposed between, a protective layer 76 laminated onto recording layer75 with a pressure-sensitive adhesive layer (not shown) interposedbetween, and a protective layer 77 laminated onto the other side ofsubstrate 74 with a pressure-sensitive adhesive layer (not shown)interposed between as shown in FIG. 9. The following provides a detailedexplanation of this optical disk 70.

(Fabrication of Substrate Sheet)

Adhesive layers composed of a pressure-sensitive adhesive were providedon both sides of paper having a thickness of 0.6 mm followed by thelamination of a resin film thereon having a thickness of 0.18 mm tofabricate a substrate sheet having a thickness of 1.1 mm.

(Fabrication of Recording Layer Sheet)

Surface irregularities corresponding to tracks and information pits weretransferred to a copper-plated roll after which the roll waschrome-plated from above to obtain a transfer mold.

An ultraviolet-cured resin was coated onto a high-density polyethylenefilm drawn to a thickness of 0.05 mm with a die coater to a thickness of0.1 mm, and the transfer mold was pressed against its surface totransfer the surface irregularities to the surface of theultraviolet-cured resin.

Next, the ultraviolet-cured resin was irradiated with ultraviolet lightto cure the ultraviolet-cured resin and form tracks.

Next, aluminum was vacuum deposited on the tracks and a light reflectinglayer having a thickness of 60 nm was formed to obtain a playback-onlytype of recording layer sheet.

(Lamination)

An acrylic pressure-sensitive adhesive was coated onto the recordinglayer sheet to a thickness of 0.005 mm by microgravure coating afterwhich it was laminated onto the other side of the substrate sheet towhich a printing sheet had been laminated.

Next, an acrylic pressure-sensitive adhesive was coated onto aprotective sheet (high-density polyethylene film drawn to a thickness of0.065 mm) to a thickness of 0.005 mm by microgravure coating after whichit was laminated onto the recording layer of the substrate sheet.

Moreover, an acrylic pressure-sensitive adhesive was coated onto aprotective sheet (high-density polyethylene film drawn to a thickness of0.065 mm) to a thickness of 0.005 mm by microgravure coating after whichit was laminated onto the back of the substrate sheet to obtain anoptical disk roll.

(Punching)

Next, the optical disk roll was punched into the shape of disks using adisk-shaped cutting blade to obtain optical disks. The optical diskswere subsequently placed between flat plates followed by the applicationof heat at 50° for 24 hours to remove any warping and obtain smoothoptical disks.

(Evaluation)

When information recorded on the resulting optical disks was read usingan optical disk drive manufactured by Pulstec Industrial Co., Ltd.(product name: DDU-1000), the information was able to be read withoutproblem.

INDUSTRIAL APPLICABILITY

An optical disk of the present invention, in which resin-impregnatedpaper in which resin is impregnated into paper, or resin-coated paper,in which the paper surface is coated with a resin, is used for thesubstrate is both environmentally friendly and inexpensive.

1. An optical disk, comprising: a substrate including resin-impregnatedpaper in which a resin has been impregnated into paper or resin-coatedpaper in which paper surface has been coated with a resin; wherein acenterline average roughness Ra of at least one side of the substrate is0.5 μm or less, and a maximum roughness Rmax is 6.0 μm or less; arecording layer provided on at least one side of the substrate whereinthe recording layer has a recording layer base material that serves as asupport for the recording layer, and the recording layer base materialincludes a non-hydrophilic film; a printing layer provided on at leastone side of the substrate, having a printing base material and a printedink applied to a surface of the printing base material facing thesubstrate; and at least one release layer provided between the substrateand the recording layer and/or between the substrate and the printinglayer, wherein the substrate has peripheral edges protected by resincoating or by attaching a resin cover and/or by being shaped into acurve.
 2. An optical disk according to claim 1, further comprising: aprotective layer to protect the recording layer.
 3. An optical diskaccording to claim 2, wherein the recording layer has a recording layerbase material that serves as a support for the recording layer, and therecording layer base material includes a non-hydrophilic film.
 4. Anoptical disk according to claim 1, wherein the at least one releaselayer includes a release layer provided between the substrate and therecording layer.
 5. An optical disk according to claim 1, wherein the atleast one release layer includes a release layer provided between thesubstrate and the printing layer.
 6. A manufacturing method of anoptical disk, comprising: recording layer sheet fabricating in which arecording layer sheet is fabricated by forming tracks on a recordinglayer base material; and recording layer sheet laminating in which arecording layer included in the recording layer sheet is provided on asubstrate including resin-impregnated paper or resin-coated paper bylaminating the recording layer sheet with resin-impregnated paper inwhich a resin is impregnated into paper or resin-coated paper in whichthe surface of the paper is coated with a resin, printing sheetfabricating in which a printing sheet is fabricated by carrying outprinting on a printing base material; and printing sheet laminating inwhich a printing layer included in the printing sheet is provided on thesubstrate including the resin-impregnated paper or resin-coated paper bylaminating the printing sheet with resin-impregnated paper in which aresin is impregnated into paper or resin-impregnated paper in which thesurface of the paper is coated with a resin, such that the printedsurface of the printing base material faces the substrate.
 7. Amanufacturing method of an optical disk according to claim 6, furthercomprising: protective film laminating in which a protective layerincluded a protective film is provided on the recording layer bylaminating the protective film onto the recording layer.
 8. Amanufacturing method of an optical disk according to any of claims 6 and7, further comprising: release layer formation in which a release layeris formed on at least one side of the resin-impregnated paper orresin-coated paper in advance.
 9. A manufacturing method of an opticaldisk according to any of claims 6 and 7, wherein each sheet is producedin the form of a wound roll, and each sheet in the form of a wound rollis laminated.
 10. A manufacturing method of an optical disk according toclaim 6, wherein the printing sheet fabrication includes printingmutually different variable information imparted to each optical diskproduced on the printing base material.
 11. An optical disk free ofbisphenol A, comprising: a substrate made of a resin-impregnated paperin which a resin has been impregnated into paper or a resin-coated paperin which at least one of the paper surfaces has been coated with aresin; a recording layer on which information is recorded and read fromusing laser light, provided on one side of the substrate; a printinglayer provided on at least one side of the substrate, having a printingbase material and a printed ink applied to a surface of the printingbase material facing the substrate, to transfer printed images; and atleast one release layer provided between the substrate and the recordinglayer and/or between the substrate and the printing layer, forseparation from the substrate during disposal, wherein the substrate hasperipheral edges protected by resin coating or by attaching a resincover and/or by being shaped into a curve.
 12. An optical disk accordingto claim 11, wherein the recording layer is one of a play-back only typeof recording layer, write-once type of recording layer, and rewritabletype of recording layer.
 13. An optical disk according to claim 11,further comprising at least one of a protective layer covering andprotecting the recording layer.
 14. An optical disk according to claim2, wherein the at least one release layer includes a release layerprovided between the substrate and the recording layer.
 15. An opticaldisk according to claim 2, wherein the at least one release layerincludes a release layer provided between the substrate and the printinglayer.